The present invention relates to a method for separating hemoglobin A2 by cation exchange liquid chromatography.
Hemoglobin A2 is composed of xcex1 and xcex4 chains, and is used, like hemoglobin F, as a diagnostic indicator of Mediterranean anemia (thalassemia). For testing of Mediterranean anemia, cation exchange liquid chromatography is generally employed to separate from a hemoglobin mixture and quantitate hemoglobin A2 (hereinafter referred to as HbA2).
Separation of a hemoglobin mixture, i.e., a hemolyzed sample, with the use of cation exchange liqud chromatography generally results in the appearance of peaks of hemoglobin A1a (hereinafter referred to as HbA1a ) and hemoglobin A1b (hereinafter referred to as HbA1b), hemoglobin F (hereinafter referred to as HbF), labile hemoglobin A1c, (hereinafter referred to as labile HbA1c), stable hemoglobin A1c (hereinafter referred to as stable HbA1c), hemoglobin A0 (hereinafter referred to as HbA0) and the like. On this occasion, an extended time has been required to achieve complete separation of HbA0 and HbA2 from each other since they show the similar retention behaviors with respect to a cation exchange column and their peaks occur in close proximity to each other.
One method of separating HbA2 from a hemoglobin (hereinafter referred to as Hb) mixture is disclosed, for example, in U.S. Pat. No. 4,810,391 which utilizes a weak cation exchange packing material and is characterized by the use of three types of buffering eluents having different phosphate concentrations and pH""s. A first eluent is a phosphate buffer maintained at a concentration of 1-20 mm and at a pH of 6.5-6.9 for use in elution of HbA1a and HbA1b. A second eluent is a phosphate buffer maintained at a concentration of 15-55 mM and at a pH of 6.4-6.8 for use in elution of HbA1c and HbA0. A third eluent is a phosphate buffer maintained at a concentration of 60-100 mM and at a pH of 6.4-6.8 for use in elution of HbA2.
EP-0315187 discloses a method for quantification of HbA2 wherein HbA1a and HbA1b are eluted by a first eluent, HbA1c and HbA0 by a second eluent and HbA2 by a third eluent.
However, in the above-described methods, the eluents are distinguished from each other substantially by the salt concentration only. This extends a measurement time and prevents quick separation and measurement of a lot of specimen, which have been problems. Another problem arises when HbA2 and HbA1c are concurrently separated and measured, i.e., precise measurement of HbA1c is disturbed significantly by the insufficient separation of HbA1cAlso, the pH""s of the eluents are lower than an isoelectric point of hemoglobin. This creates another problem, i.e., increases the tendency of Hb and other blood components to be adsorbed on packing material to thereby shorten a column service life.
In view of the above-described problems encountered in conventional methods of separating HbA2 from a Hb mixture, an object of the present invention is to provide a method which enables quicker and more precise separation of HbA2 than conventional methods.
A first invention of the present application is a method for separating hemoglobin A2 from a hemoglobin mixture by cation exchange chromatography, characterized in that at least two types of eluents are used including an eluent (eluent A) for elution of faster hemoglobins than hemoglobin A0 and an eluent (eluent B) for elution of hemoglobin A0 and slower hemoglobins than hemoglobin A0, and that the eluent A has a pH of 4.0-6.0 and the eluent B is maintained at a pH of at least 0.5 higher than that of the eluent A.
In a particular aspect of the first invention, the eluent B is maintained at a salt concentration lower than that of the eluent A.
In a more limited aspect of the first invention, an eluent (eluent D) is further used for elution of at least hemoglobin A2. The eluent D is maintained at a pH of at least 0.5 lower than that of the eluent B.
In a more limited aspect of the first invention, a salt concentration of the eluent B is rendered lower than that of the eluent A and a salt concentration of the eluent D is rendered higher than that of the eluent B.
In a further particular aspect of the first invention, an eluent (eluent C) is further used having an elution power weaker than those of the eluents B and D. Those eluents are delivered in the sequence of B, C and D.
In a further particular aspect of the first invention, an eluent (eluent H) at a pH of 6.8-12 is delivered to follow the eluent B, or alternatively, to follow the eluent D when the eluents B and D are used in combination. The eluent H preferably contains a chaotropic ion.
A second invention of the present application is a method for separating hemoglobin A2 from a hemoglobin mixture by cation exchange chromatography, characterized by the use of at least two types of eluents including an eluent (hereinafter referred to as xe2x80x9celuent Exe2x80x9d) which contains a chaotropic ion and also contains an inorganic acid, organic acid and/or any salt thereof having a buffer capacity at a pH of 4.0-6.8 and an eluent (hereinafter referred to as xe2x80x9celuent Fxe2x80x9d) which contains an inorganic acid, organic acid and/or any salt thereof having a buffer capacity at a pH of 6.5-8.0.
In a particular aspect of the second invention, an eluent (hereinafter referred to as xe2x80x9celuent Gxe2x80x9d) is further used having a lower pH and a higher salt concentration than the eluent F. The eluent G is delivered to follow the eluent F.
In a further aspect of the second invention, an eluent (eluent H) at a pH of 6.8-12 is delivered to follow the eluent F or G. Preferably, the eluent H contains a chaotropic ion.
In another particular aspect of the first or second invention, an azide ion is incorporated in at least one type of eluent and/or a hemolyzing solution.
In a further particular aspect of the first or second invention, a packing material is employed having at least one type of strong cation exchange group.
The first invention is now described.
In the first invention, xe2x80x9can eluent (referred to in this specification as xe2x80x9celuent Axe2x80x9d) used to elute faster hemoglobins than hemoglobin A0xe2x80x9d refers to the eluent used to elute Hb""s that exhibit shorter retention time than HbA0while the hemoglobin mixture is subjected to separation by cation exchange liquid chromatography. General examples of Hb""s to be eluted by the eluent A include HbA1a, HbA1b, HbF, labile HbA1c, stable HbA1c and the like. It should be understood that not all of the above-listed Hb""s but at least one type thereamong is needed to be eluted by the eluent A. The first invention, while its primary object is to separate HbA2, also enables the separation and quantitation of stable HbA1c by performing elution of HbA1a, HbA1b, HbF, labile HbA1c and stable HbA1c with the aid of the eluent A.
The eluent A has a pH of 4.0-6.0, preferably of 4.5-5.8. If a pH of the eluent A is below 4.0, denaturation of hemoglobin may be caused to occur. If a pH of the eluent A exceeds 6.0, hemoglobins may be charged less positively to reduce its tendency to be retained by the cation exchange group, resulting in its reduced resolution. The eluent A is not necessarily a single type of eluent, and may be an eluent group A consisting of plural types of eluents having differing compositions and elution powers (in the case where the eluent A consists of n types of eluents, they are hereafter designated xe2x80x9celuent A1, eluent A2, . . . , eluent Anxe2x80x9d), so long as the eluent group A satisfies the above-specified conditions required for the eluent A. When desired to separate and quantitate stable HbA1c, as well as HbA2, within a shorter period of time, the eluent components A1, A2, A3 and the like may be delivered in a sequence of increasing elution power according to a linear gradient elution technique, a stepwise gradient elution technique or a combination thereof.
In the first invention, xe2x80x9can eluent (referred to in this specification as the xe2x80x9celuent Bxe2x80x9d) used to elute hemoglobin A0 and slower hemoglobins than hemoglobin A0 xe2x80x9d refers to the eluent used to elute HbA0 and Hb""s that exhibit the same retention time or longer retention time than HbA0 while the hemoglobin mixture is subjected to separation by the cation exchange liquid chromatography. General examples of Hb""s to be eluted by the eluent B include HbA0, HbA2, HbS, HbC and the like. It should be understood here that not all of the above-listed Hb""s is needed to be eluted by the eluent B. The first invention may employ the eluents A and B only. In such a case, the eluent B is used to elute HbA0, HbA2 and the like. In the below-described case where an eluent D is used to elute HbA2, the eluent B may be used to elute at least HbA0. The eluent B may further elute stable HbA1c and labile HbA1c, so long as the elution of at least HbA0 is assured. Particularly when quantitation of HbF and HbA2 only are effected, the elution of stable HbA1c by the eluent B permits quicker separation.
Characteristically, the pH of the eluent B is rendered higher than that of the eluent A by at least 0.5. This is because the pH of the eluent B, if rendered at least 0.5 higher than that of the eluent A, improves resolution of HbA0. and HbA2. More preferably, the pH of the eluent B is rendered at least 0.8 higher than that of the eluent A. The pH of the eluent B is preferably in the range of 6.0-8.0, i.e., in the neighborhood of a hemoglobin""s isoelectric point (the Encyclopedia of Physics and Chemistry (4th ed., Iwanami Shoten, September 1987, edited by Ryogo Kubo et al.), at page 1178, describes the isoelectric point of hemoglobin as being pH 6.8-7.0). The eluent B is not necessarily a single type of eluent, and may be an eluent group B that consists of plural types of eluents having different compositions and elution powers (in the case where the eluent B consists of n types of eluents, they are hereafter designated xe2x80x9celuent B1, eluent B2, . . . , eluent Bnxe2x80x9d), so long as the eluent group B satisfies the above-specified conditions required for the eluent B.
In the first invention, a salt concentration of the eluent B is preferably made lower than that of the eluent A. The salt concentration of an eluent, as used herein, means a total concentration of cations present in the eluent. The salt concentration of the eluent B, if rendered lower than that of the eluent A, further improves resolution of HbA0 and HbA2. The salt concentration of the eluent B is preferably made lower than that of the eluent A by at least 10 mM, more preferably by at least 30 mM.
Other than the eluents A and B, an additional eluent (referred to in the present specification as xe2x80x9celuent Dxe2x80x9d) may preferably be used to elute at least hemoglobin A2. The use of this eluent D further improves the resolution between HbA2 and HbA0 and also between HbA2 and slower hemoglobins than HbA2. This eluent D suffices if effective to elute at least HbA2. Accordingly, in the case where the eluent D is effective to elute HbA2 only, HbS, HbC and the like may be eluted either by the eluent D or another eluent, for example, by an eluent H as will be described below.
Characteristically, the pH of the eluent D is rendered lower than that of the eluent B by at least 0.5. The pH of the eluent D, if rendered at least 0.5 lower than that of the eluent B, further improves the resolution between HbA2 and HbA0, and also between HbA2 and slower hemoglobins than HbA2. More preferably, the pH of the eluent D is rendered lower than that of the eluent B by at least 0.8. The eluent D is not necessarily a single type of eluent, and may be an eluent group D which consists of plural types of eluents having differing compositions and elution powers (in the case where the eluent D consists of n types of eluents, they are hereafter designated xe2x80x9celuent D1, eluent D2, . . . , eluent Dnxe2x80x9d), so long as the eluent group D satisfies the above-specified conditions required for the eluent D. The use of such an eluent group D not only permits precise separation of HbA2 within a short period of time, but also enables separation and quantitation of HbS, HbC and the like.
In the case where the eluent D is used, it is preferred that the eluent B is kept at a salt concentration lower than that of the eluent A and that the eluent D is kept at a salt concentration higher than that of the eluent B. Preferably, the eluent B is maintained at a salt concentration at least 10 mM lower than that of the eluent A while the eluent D is maintained at a salt concentration at least 10 mM higher than that of the eluent B. More preferably, the eluent B is maintained at a salt concentration at least 30 mM lower than that of the eluent A while the eluent D is maintained at a salt concentration at least 30 mM higher than that of the eluent B.
In the first invention, besides the eluents A, B and C, an additional eluent (referred to in this specification as xe2x80x9celuent Cxe2x80x9d) may further be used having a weaker elution power than the eluents B and D. In this case, those eluents can be delivered in the order of B, C and D. The use of such an eluent C retards elution of HbA2 so that the more precise separation of HbA2 can be achieved.
The eluent C may be maintained at any pH, so long as it has a weaker elution power than the eluents B and D. The eluent having a weak elution power, as used herein, refers to the eluent effective to retard elution of Hb""s when the hemoglobin mixture is subjected to separation by cation exchange liquid chromatography. An elution power of an eluent can be weakened by various techniques, including reduction of a pH or salt concentration of the eluent. In the present case, the eluent C is rendered lower than the eluents B and D, in terms of either or both of a pH and a salt concentraion.
In the first invention, the eluents are delivered in the order of A and B, or in the order of A, B and D if D is also used, or in the order of A, B, C and D if C is also used. In general, the elution power is controlled to increase in the order of A, B and D.
The above-described eluents A-D (hereinafter referred to as xe2x80x9celuentxe2x80x9d, collectively, in the description of the first invention), for use in the first invention, comprise a buffer. The buffer may be used in the form of containing suitable additives which will be described later. Examples of buffer agents contained in the buffer include inorganic acids, organic acids and salts thereof which are illustrated below.
Examples of inorganic acids include phosphoric acid, boric acid, carbonic acid and the like.
Examples of organic acids include carboxylic acids, dicarboxylic acids, carboxylic acid derivatives, hydroxy-carboxylic acids, amino acids, amines, imidazoles, pyridine, cacodylic acid, tris(hydroxymethyl)aminomethane, glycyl-glycine, pyrophosphoric acid and the like.
Examples of carboxylic acids include acetic acid, propionic acid and the like.
Examples of dicarboxylic acids include malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, phthalic acid and the like.
Examples of carboxylic acid derivatives include xcex2,xcex2-dimethyl glutaric acid, barbituric acid, aminobutyric acid and the like.
Examples of hydroxycarboxylic acids include tartaric acid, citric acid, lactic acid and the like.
Examples of amino acids include aspartic acid, asparagine, glycine and the like.
Examples of amines include ethylenediamine, triethanol-amine and the like.
Examples of imidazoles include imidazole, 5(4)-methyl-imidazole, 2,5 (4)-dimethylimidazole and the like.
Examples of salts of inorganic or organic acids are known in the art, including sodium and potassium salts.
Examples of buffer agents include 2-(N-morpholino) ethanesulfonic acid (MES), N-2-hydroxyethylpiperazine-Nxe2x80x2-2-ethanesulfonic acid (HEPES), bis(2-hydroxyethyl)iminotris-(hydoxylmethyl)methane (Bistris), Tris, ADA, PIPES, Bistris-propane, ACES, MOPS, BES, TES, HEPES, HEPPS, Tricine, Bicine, glycylglycine, TAPS, CAPS and the like, which generally constitute a Good""s buffer. Other useful buffers include Britton and Robinson""s buffer and GTA buffer.
The above-listed inorganic acids, organic acids and their salts may be used alone or in combination. Also, the above-listed inorganic acids and organic acids may be used in combination.
The concentration of the buffer agent in the eluent is not particularly specified, so long as its buffer action is effective in water. It is preferably in the range of 0.1-1,000 mM, more preferably in the range of 1-500 mM.
The eluent may also contain (1) an inorganic salt, (2) a chaotropic ion, (3) a pH adjustor, (4) a water-soluble organic solvent and the like, which are listed below.
(1) Inorganic salt: Examples of inorganic salts include sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, sodium phosphate and the like. While not particularly limited, they may preferably be incorporated in the amount of 1-1,500 mM.
(2) Chaotropic ion: Specific examples of chaotropic ions are listed in the subsequent description of an eluent E for use in the second invention. The concentration of the chaotropic ion in the eluent is preferably in the range of 0.1 mM-3,000 mM, more preferably in the range of 1 mM-1,000 mM, most preferably in the range of 10 mM-500 mM.
(3) pH adjustor: Known acids or bases may be used as pH adjustors. Examples of acids include hydrochloric acid, phosphoric acid, nitric acid, sulfuric acid and the like. Examples of bases include sodium hydroxide, potassium hydroxide, lithium hydroxide, magnesium hydroxide, barium hydroxide, calcium hydroxide and the like. While not limiting, these acids or bases may preferably be added in concentrations of 0.001-500 mM.
(4) Water-soluble organic solvent: Examples thereof include methanol, ethanol, acetonitrile, acetone and the like. Although not limiting, these organic solvents may preferably be added in concentrations of 0-80 % by volume. Preferably, their concetrations are maintained at levels insufficient to cause deposition of the chaotropic ion, inorganic acid, organic acid or any salt thereof used.
The second invention is now described.
In the second invention, at least two types of eluents are utilized including an eluent (referred to in this specification as xe2x80x9celuent Exe2x80x9d) which contains a chaotropic ion and also contains an inorganic acid, an organic acid and/or any salt thereof having a buffer capacity at a pH of 4.0-6.8, and an eluent (referred to in this specification as xe2x80x9celuent Fxe2x80x9d) which contains an inorganic acid, an organic acid and/or any salt thereof having a buffer capacity at a pH of 6.5-8.0.
The eluent E contains a chaotropic ion. The chaotropic ion is produced via dissociation of compounds in an aqueous solution. It destroys a structure of water and suppresses the entropy reduction of water that occurs upon contact with a hydrophobic material. Examples of negative chaotropic ions include a tribromoacetate ion, trichloroacetate ion, thiocyanate ion, iodide ion, perchlorate ion, dichloro-acetate ion, nitrate ion, bromide ion, chloride ion, acetate ion and the like. Other examples are urea and the like. Examples of positive chaotropic ions include a barium ion, calcium ion, magnesium ion, lithium ion, cesium ion, potassium ion, guanidine ion and the like.
The use of the following chaotropic ions, among the above-listed ions, is preferred for their ability to improve separation precision; negative ions such as a tribromo-acetate ion, trichloroacetate ion, thiocyanate ion, iodide ion, perchlorate ion, dichloro-acetate ion, nitrate ion and bromide ion; and positive ions such as a barium ion, calcium ion, magnesium ion, lithium ion, cesium ion and guanidine ion. Particularly preferred are a tribromoacetate ion, trichloroacetate ion, iodide ion, thiocyanate ion, perchlorate ion, nitrate ion and guanidine ion.
The concentration of the chaotropic ion present in the eluent E is preferably in the range of 0.1 mM-3,000 mM, more preferably in the range of 1 mM-1,000 mM, and most preferably in the range of 10 mM-500 mM. If it is below 0.1 mM, a separating effect may be reduced to result in the poor measurement precision. If it exceeds 3,000 mM, the effect of separating hemoglobins shows no further improvement. The above-listed chaotropic ions may be used alone or in combination.
The eluent E further contains an inorganic acid, an organic acid and/or any salt thereof having a buffer capacity at a pH of 4.0-6.8. Any of those listed in the preceding first invention as buffer agents, if having a buffer capacity at a pH of 4.0-6.8, can be used for such an inorganic acid, an organic acid and/or any salt thereof.
The concentration of the buffer agent in the eluent E is adjusted such that it exhibits a sufficient buffer action in water to maintain the eluent at a pH of 4.0-6.8. It is preferably in the range of 1 mM-1,000 mM, more preferably in the range of 10 mM-500 mM.
The eluent E is maintained at a pH of 4.0-6.8, preferably of 4.5-5.8. If a pH of the eluent E is below 4.0, denaturation of hemoglobin may be caused to occur. If it exceeds 6.8, hemoglobins may be charged less positively to reduce their tendencies to be retained by the cation exchange group, resulting in the reduced resolution.
The eluent F contains an inorganic acid, an organic acid and/or any salt thereof having a buffer capacity at a pH of 6.5-8.0, which are illustrated below.
Examples of inorganic acids include phosphoric acid and boric acid. Examples of organic acids include dicarboxylic acids, hydroxycarboxylic acids, amino acids, imidazoles, amines, alcohols and the like.
Examples of dicarboxylic acids include maleic acid, malonic acid, succinic acid and the like. Examples of hydroxycarboxylic acids include citric acid and the like. Examples of amino acids include asparagine, histidine and the like. Examples of imidazoles include 5(4)-hydroxy-imidazole, imidazole, 5(4)-methylimidazole, 2,5(4)-dimethyl-imidazole and the like. Examples of amines include ethylenediamine, diethanolamine, ethanolamine and the like.
Examples of alcohols include 2-amino-2-methyl-1,3-propanediol, 2-amino-2-ethyl-1,3-propanediol and the like.
Also useful are 2,4,6-collidine, N-ethylmorpholine, morpholine, 4-aminopyridine, pyrophosphoric acid, cacodylic acid, 5,5-diethyl barbituric acid, xcex2, xcex2xe2x80x2-dimethyl glutaric acid, glycerol phosphate and the like.
A Good""s buffer is also useful, including MES, Bistris, ADA, PIPES, Bistris propane, ACES, BES, MOPS, TES, HEPES, HEPPS, Tris, Tricine, glycylglycine, Bicine, TAPS and the like, for example.
The salts of inorganic and organic acids are known in the art and include sodium salts, potassium salts and the like, for example.
The above-listed inorganic acids, organic acids and/or their salts may be used alone or in combincation. The above-listed inorganic and organic acids may be used in combination.
The concentration of the buffer agent in the eluent F is adjusted such that it exhibits a sufficient buffer action in water to maintain the eluent at a pH of 6.5-8.0. It is preferably in the range of 1 mM-1,000 mM, more preferably in the range of 10 mM-500 mM.
The eluent F is maintained at a pH of 6.5-8.0, preferably of 6.7-7.8. This is because separation of hemoglobin A2 becomes insufficient if the pH of the eluent F falls below 6.5 or exceeds 8.0.
Besides the eluents E and F, the second invention further uses an eluent (referred to in this specification as xe2x80x9celuent Gxe2x80x9d) which has a lower pH and a higher salt concentration than the eluent F. The eluent G may be delivered to follow the eluent F.
The eluent G is preferably maintained at a pH lower than that of the eluent F by 0.1-5.0, more preferably by 0.5-4.0, most preferably by 1.0-3.0. Unless the pH of the eluent G is rendered at least 0.1 lower than that of the eluent F, poor separation of hemoglobin A2 may result. Unless it is rendered at most 5.0 lower than that of the eluent F, denaturation of hemoglobin may be caused to occur, resulting in the poor hemoglobin measurement precision.
The eluent G is also maintained at a salt concentration higher than that of the eluent F. The salt concentration is represented in terms of a total concentration of cations present in each eluent. The eluent G is preferably maintained at a salt concentration higher than that of the eluent F by 0.5 mM-200 mM, more preferably by 1 mM-175 mM, most preferably by 5 mM-150 mM. Unless the salt concentration of the eluent G is rendered at least 0.5 mM higher than that of the eluent F, insufficient elution of hemoglobin A2 may result. Unless it is rendered at most 200 mM higher than that of the eluent F, poor separation of hemoglobin A2 may result.
The eluent G may contain, as a buffer agent, such an inorganic acid, organic acid and/or any salt thereof having a buffer capacity at a pH of 4.0-6.8 as incorporated in the eluent E. Preferably, a chaotropic ion may be added to the eluents F and G, as similar to the eluent E.
In the second invention, the eluent E, F or G may further contain (1) an inorganic salt, (2) a pH adjustor, (3) a water-soluble organic solvent, (4) a stabilizer, (5) amine, (6) a surfactant and the like, which are illustrated below.
Those additives described to be useful for the eluent in the first invention can also be used for (1) inorganic salt, (2) pH adjustor and (3) water-soluble organic solvent.
(4) Hemoglobin Stabilizer: Examples of stabilizers include chelating agents such as ethylenediaminetetraacetic acid (EDTA), and reducing agents/antioxidants such as glutathione.
(5) Amine: A primary purpose of amine addition is to suppress the nonspecific adsorption of hemoglobin. Useful amines are known in the art. The use of primary, secondary and tertiary amines having melecular weights of 20-500 is preferred.
(6) Surfactant: Examples of surfactants include nonionic, cationic and anionic surfactants. The use of the surfactant permits efficient hemolysis and is effective to clean a flow path through which a hemolyzed sample is passed during measurement such as by high-performance liquid chromatography (HPLC). Preferred among the above-listed surfactants are nonionic surfactants. Examples of nonionic surfactants include polyoxyethylenes (polyoxyethylene is hereinafter referred to as POE, and the number of moles of ethylene oxide added is represented by (n)), POE(7) decyl ether, POE(n) dodecyl ether, POE(10) tridecyl ether, POE(11) tetradecyl ether, POE(n) cetyl ether, POE(n) stearyl ether, POE(n) oleyl ether, POE(17) cetylstearyl ether, POE(n) octyl phenyl ether, POE(n) nonylphenyl ether, sorbitan mono-laurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate, POE(n) sorbitan monolaurate, POE(n) sorbitan monopalmitate, POE(n) sorbitan monostearate, POE(n) sorbitan monooleate and the like.
The above-listed surfactants may be used alone or in combination. Preferably, these surfactants may be added in the amount of 0.01-10 % by weight.
The constitution common to the first and second inventions (hereinafter referred to as xe2x80x9cpresent inventionxe2x80x9d, collectively) is now described.
In the present invention, an eluent (referred to in this specification as eluent xe2x80x9cHxe2x80x9d) at a pH of 6.8-12 is preferably delivered for the primary purpose of cleaning a column. The pH of the eluent H is such specified because of the following reasons. If below 6.8, the eluent H while passed through the column may fail to reach a pH equal to an isoelectric point of hemoglobin, resulting in the failure to clean the column effectively. If above 12, decomposition of a packing material may be caused to occur. More preferably, the eluent H is maintained at a pH of 7.5-11. The pH range of 8.0-9.5 is particularly preferred. However, the pH of the eluent H may be permitted to exceed 12, in the case where measurement is unaffected by decomposition of a packing material.
The eluent H may comprise, for example, a buffer containing an inorganic acid or its salt such as phosphoric acid, boric acid and carbonic acid; hydroxycarboxylic acid such as citric acid; carboxylic acid derivative such as xcex2,xcex2-dimethylglutaric acid; dicarboxylic acid such as maleic acid; or an organic acid or its salt such as cacodylic acid.
Examples of buffers include 2-(N-morpholino) ethane-sulfonic acid (MES), N-2-hydroxyethylpiperazine-Nxe2x80x2-2-ethanesulfonic acid (HEPES), bis(2-hydroxyethyl) iminotris-(hydoxylmethyl)methane (Bistris), Tris, ADA, PIPES, Bistris-propane, ACES, MOPS, BES, TES, HEPES, HEPPS, Tricine, Bicine, glycylglycine, TAPS, CAPS and the like, which generally constitute a Good""s buffer. Other useful buffers include Britton and Robinson""s buffer and GTA buffer. Also useful are organic substances, including imidazoles such as imidazole; amines such as diethanolamine and triethanol-amine; amino acids such as glycine and the like. These inorganic acids, organic acids and their salts may be used in combination. Alternatively, such inorganic and organic acids may be used in combination.
The above-listed inorganic acids., organic acids and their salts may be incorporated in the eluent H within the concentration range that allows them to exhibit sufficient buffer actions in water to keep the eluent H at a pH of at least 6.8, i.e., preferably within the concentration range of 1 mM-1,000 mM, more preferably of 10 mM-500 mM.
Preferably, a chaotropic ion may preferably be added to the eluent H to achieve a more effective column cleaning. Useful chaotropic ions are listed above. The chaotropic ion concentration is preferably in the range of 1 mM-3,000 mm, more preferably in the range of 10 mM-1,000 mM, most preferably in the range of 50 mM-500 mM.
Like the above-described eluents E, F and G, the eluent H may further contain various additives, including, for example, (1) an inorganic salt, (2) a pH adjustor, (3) a water-soluble organic solvent, (4) a stabilizer, (5) amine, (6) a surfactant and the like.
In the first invention, in the case where the eluent H is used, the eluents may be delivered in the order of A, B and H, or in the order of A, B, D and H, or in the order of A, B, C, D and H. In the second invention, in the case where the eluent H is used, the eluents may be delivered in the order of E, F and H, or in the order of E, F, G and H.
Also in the present invention, it is more preferred that an azide ion be added to at least one eluent selected from the eluents A-H. This azide ion may be added to a hemolyzing solution. The azide ion may be added to either or both of the eluent and hemolyzing solution. The azide ion may be added in the form of its salt which dissociates in an aqueous solution to produce azide ions. Useful azide salts are known in the art. The use of sodium azide, barium azide or the like is preferred.
The azide ion concentration in the eluent or hemolysed solution is preferably in the range of 0.001-0.5 % by weight, more preferably in the range of 0.005-0.4 % by weight. If the concentration is below 0.001 % by weight, an effect of improving resolution can not be obtained. If it exceeds 0.5 % by weight, no further resolution improvement can not be expected.
A packing material, for use in the cation exchange liquid chromatography according to the present invention, comprises particles having at least one type of cation exchange group. Such particles can be prepared, for example, by introducing cation exchange groups into polymer particles.
Examples of cation exchange groups are known in the art, and include a carboxyl group, a sulfonic acid group, a phosphoric acid group and the like. Any combination of such cation exchange groups may be introduced.
Preferably, a packing material is utilized having at least one type of strong cation exchange group. This strong cation exchange group refers to a cation exchange group which exhibits an ion exchange action even in an eluent maintained at an approximate pH of 2-3, such as a sulfonic acid group among those listed above. The use of the packing material having at least one strong cation exchange group reduces an eluent pH to such a degree that allows hemoglobins to be charged more positively and increases their tendency to be retained by a column, resulting in the increased resolution.
The above-described particles have diameters preferably in the range of 0.1-20 xcexcm, more preferably in the range of 0.2-8 xcexcm. The particle size distribution is preferably 40% or less, more preferably 30% or less, when represented by a coeffeicient of variation (CV value)(=(a standard deviation of a particle size distibution)/(its arithmetic mean)xc3x97100 (%))
Examples of such polymer particles include inorganic particles such as silica and zirconia; natural polymer particles such as cellulose, polyamino acid and chitosan; synthetic polymer particles such as polystyrene and polyacrylate; and the like.
Preferably, the polymer particle constituents, other than the introduced cation exchange group, are relatively hydrophilic. In view of the resistance to pressure and swelling, those constituents preferably have higher crosslinking levels.
A cation exchange group can be introduced into polymer particles by any known technique. For example, a technique can be utilized which comprises, in sequence, preparing polymer paticles having functional groups (such as hydroxyl, amino, carboxyl and epoxy) and allowing the functional groups to undergo a chemical reaction so that cation exchange groups are introduced into the polymer particles.
Alternatively, a cation exchange packing material may be prepared by a technique that produces polymer particles via polymerization of a monomer having a cation exchange group. For example, a technique can be utilized which involves mixing a cation exchange group-containing monomer with a crosslinking monomer and allowing the mixture to polymerize in the presence of a polymerization initiator.
Another applicable technique encompasses mixing polymerizable ester containing a cation exchange group, such as methyl (meth)acrylate and ethyl (meth)acrylate, with a crosslinking monomer; allowing the mixture to polymerize in the presence of a polymerization initiator; and subjecting the resulting polymer particles to hydrolysis so that the ester is converted into a cation exchange group.
Japanese Patent Publication No. Hei 8-7197 discloses a further applicable technique which comprises, in sequence, preparing crosslinked polymer particles, adding thereto a cation exchange group-containing monomer, and allowing the monomer to polymerize in the vicinity of polymer particle surfaces.
The above-described packing material is packed into a column for use in the liquid chromatographic measurement. The column is preferably sized to have an inner diameter of 0.1-50 mm and a length of 1-300 mm. More preferably, it measures an inner diameter of 0.2-30 mm and a length of 5-200 mm. If the column measures below 0.1 mm in inner diameter and below 1 mm in length, poor operability and resolution results. On the other hand, if the column measures above 50 mm in internal diameter and above 300 mm in length, the increased amount of packing material is required. Poor resolution also results.
Although any known technique can be utilized for packing the material into a column, the use of a slurry packing technique is preferred. Illustrating a specific example, packing material particles are dispersed in a buffer, such as an eluent, to provide a slurry which is subsequently injected into a column as by a delivery pump.
The column can be formed from materials known in the art, including metals such as stainless steel, glasses, resins such as PEEK (polyether ether ketone), and the like. Preferably, a portion of the column, e.g., an inner surface, that contacts with packing materials may be covered with an inert material. Examples of such inert materials include PEEK, polyethylene, Teflon, titanium compounds, silicon compounds, silicone films.
The column may be used in combination with a filter or a prefilter at least surface of which is formed from an inert material. Examples of such inert materials include cellulose ester, cellulose acetate, cellulose triacetate, cellulose, cellulose nitrate, polytetrafluoroethylene, polyvinylidene difluoride, polysulfone, polyethylene, polyether ether ketone, polyether sulfone, polypropylene, nylon, polyvinylidene fluoride, glass materials, acrylic copolymers, oxide ceramics, carbide ceramics, nitride ceramics, silicide ceramics, boride ceramics, titanium and the like. These materials can be used in any suitable combination. In the case where stainless steel and other materials are used which are not inert in nature, a suitable technique may be utilized whereby they are covered with an inert material, or they are rendered inert as by a treatment with silicone, or they are blocked with a blocking agent such as bovine serum albumin, gelatin, casein, globulin or hemoglobin.
Liquid chromatography for use in the separation method of the present invention is known in the art, and generally employs a delivery pump, a sample injecting equipment (sampler), a column and a detector. Other suitable auxiliary equipments (such as a column oven and an eluent degasser) may also be attached.
In the present invention, for liquid chromatography, a semimicro system can be used including liquid contacting parts, e.g., a pump, a mixing column, a sampler, pipings, a prefilter (holder, filter), a column and a detector (cell), which are reduced in dead volume to the minimum. The mixing column is preferably reduced in size to less than 500 xcexcl, more preferably to less than 250 xcexcl. An injection valve for the sampler is preferably reduced in volume to less than 10 xcexcl, more preferably to less than 5 xcexcl, most preferably to less than 2 xcexcl. An inner diameter of the piping is preferably reduced to less than 0.25 mm, more preferably to less than 0.13 mm, most preferably to less than 0.065 mm. In the case where the sampler, prefilter, column, detector and the like are connected by pipings, such pipings are preferably reduced in length to the minimum. The detector (cell) is preferably reduced in volume to less than 20 xcexcl, more preferably to less than 10 xcexcl, most preferably to less than 5 xcexcl The delivery pump preferably has the ability to supply a stable flow with least pulsation. More precise separation can be achieved within a short period of time when the liquid contacting parts are formed from inert materials, such as Teflon and PEEK, and an interior dead volume of the equipment is minimized.
An exemplary construction of the liquid chromatograph used to perform separation according to a stepwise gradient elution technique is shown in FIG. 1. Eluents a, b, c and d have differing elution powers. A solenoid valve 1 is opened at a specific time interval to allow deliver of each eluent. The eluent and a sample from a sample injection port 3 are fed together into a column 4 by the action of a delivery pump 2. Various components present in the sample are detected by a detector 5. An area, height and others of each peak are calculated by an integrator 6.
Other conditions for use in the separation method of the present invention are known in the art. Each eluent is preferably delivered at a flow rate of 0.05-5 ml/min, more preferably of 0.2-3 ml/min. In the case where the above-described semimicro equivalent system is used, each eluent is preferably delivered at a flow rate of 0.001-3 ml/min, more preferably of 0.01-1.8 ml/min, further preferably of 0.03-1 ml/min. It is difficult to stabilize the flow rate if slower than 0.001 ml/min. If the flow rate exceeds 3 ml/min, the separation precision may be lowered.
Various techniques, without limitation, can be utilized to deliver an eluent for use in the separation method of the present invention, including a linear gradient elution technique and a stepwise gradient elution technique, for example.
While not particularly limited, the detection of hemoglobins is preferably performed by a 415 nm visible light.
The hemoglobin mixture to be separated by the present method is generally prepared by diluting a hemolyzed solution obtained via hemolysis with a hemolytically active substance such as a surfactant. The amount of the hemoglobin mixture injected to the liquid chromatograph is varied depending upon the dilution ratio, but is preferably in the approximate range of 0.1-100 xcexcl.